The long-term objectives are to understand how multiple forms of steroid hormone receptors help to orchestrate the development of complex tissues such as the central nervous system (CNS). The insect CNS is an excellent model system in which the steroid hormones, the ecdysteroids, act during metamorphosis to evoke neuronal remodeling, programmed cell death, and maturation of immature neurons. This diversity of cell responses is matched by a similar diversity of ecdysteroid receptor (EcR) subtypes. The significance and control of EcR expression will be examined using Drosophila melanogaster and the tobacco hornworm moth, Manduca sexta. Patterns of EcR change are very similar in the two species; the molecular and genetic power of Drosophila can then be combined with the ease of endocrine manipulation and cellular analysis of identified neurons in Manduca. The specific aims are: 1.) To characterize the EcR gene of Manduca and the types of transcripts that it produces. Specific antibody and nucleotide probes that identify the various EcR subtypes will be generated. 2.) To examine the changes in the various EcR subtypes in identified neurons through metamorphosis by in situ hybridization and immunocytochemistry. These studies will help establish the relationship of receptor dynamics with particular developmental fates. 3.) To examine the endocrine control over the dynamics of the larval EcR subtype and the transition from one subtype to another as metamorphosis progresses, using both in vitro and in vivo approaches. 4.) To determine the effect of inappropriate expression of EcR subtypes by using Drosophila transformant lines that carry the various subtypes of EcR under the control of an inducible promoter. 5.) To begin an examination of the relationship of EcR expression to the activation of "early" genes that mediate ecdysteroid action.